Conventional mobile telephone handsets include a keypad and an LCD display device which are provided with internal back lighting which is switched on for a period when the keys are operated. During manufacture, the mobile telephone handset undergoes a functional test to determine that the LCD display device operates satisfactorily.
The functional testing involves applying test signals to the handset from an external test signal generator, which causes the LCD device to be switched on. An electronic image capture device is used to record an image of the handset under test and the resulting image is processed according to a highly complex analytical technique to determine whether the LCD is functional. Analysis of the captured image is complex due to the fact that the LCD is subject to back and other spurious lighting that varies in a non-linear manner across its display area.
The present invention seeks to provide an improved, simpler approach.